A420 Gr WPL6 impact test temperature documentation & unit systems 3

[gwalkerb]

We are building ASME B31.3 piping for a compressor package where our customer has specified an MDMT of -50F for certain outdoor applications. We are using the typical materials A333 Gr 6, A420 Gr WPL6, and A350 Gr LF2 Class 1 for this system. Our QC department has raised a concern as the MTRs for some of this material specify the test temperature only in Celcius, at -45C (the specific example is A420 Gr WPL6). When this is converted to Fahrenheit, it's only -49F. However, the material specifications for the aforementioned materials all note that when material is ordered to the non-M version of the spec (i.e. A420, not A420M), the system of units is to be the inch-pound system, and temperatures would be specified in Fahrenheit. It also notes that converting between the two unit systems can lead to a non-conformance. The manufacturer's MTR specifies compliance to all four of A420, SA-420, A420M, and SA-420M.

I would interpret the requirements of that material spec to require the impact testing temperature to be listed in both -50F (to meet A420), and -45C (to meet A420M). Otherwise, I don't believe this material properly meets the listed specifications.

We are confirming with the customer if they would accept an MDMT of -49F instead of -50F, but if we aren't successful there, I'm wondering what the recommended way to resolve this issue would be. While we can go back to our supplier, and have them go back to the original manufacturer, I'm hoping we can avoid this somehow, as we have a lot of material that falls into this category, that's come from many different mills.

 

[EdStainless]

If the MDMT is -50F why did you only ask for testing at -50F?
I would have asked for -55F.
And yes, if your order said -50F then they obliged to report in "F".
They can also show as many other sets of units as they want to, but the one that you asked for must be one of them.
I hope that they didn't do this also with thickness.
In ASTM those are not hard conversions, and it is easy to make a size that doesn't meet both M and non-M.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[jmec87]

This will have zero effect on the real life safety of the system. Whether the impact test was carried out at -45.0°C (-49.0°F) or -45.6°C (-50.0°F), if it passed, the material will be fine at -50.0°F. Wasting effort and causing stress over something that doesn't matter is not a good use of resources, although I do understand the need to prevent hassle from customers and regulators.

Note that B31.3-2020 Table A-1M lists the minimum temperature for A420 WPL6 as -46°C (-50.8°F). This is lower than both the -45°C and the -50°F shown in A420. A reasonable person will accept that ASTM and ASME have divergent views on whether -50°F is equivalent to -45°C or -46°C and that it doesn't matter in service.

If the MDMT is -50F why did you only ask for testing at -50F?

-50°F is the specified impact test temperature in A420 for WPL6. Asking for -55°F would make it non-standard A420. ASME B31.3 Table A-1 lists the minimum temperature for A420 WPL6 as -50°F.

If you want to push this back on your material suppliers, check whether you ordered A420 or dual-certified A420/A420M:

This specification is expressed in both inch-pound units and in SI units. However, unless the order specifies the applicable "M" specification designation (SI units), the material shall be furnished in inch-pound units.

The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

If you only ordered A420, they should give you MTRs that conform to A420. Hopefully their testing conforms to both A420 and A420M, and they'll be able to give you an A420-conformant MTR. However, if you ordered A420/A420M, then they likely conformed to the order requirements if they reported all results in SI units, but maybe they can still give you an MTR with inch-pound units reported.

 

[SWComposites]

Oh cripe, what is the accuracy of the thermometer used during the test? I doubt its even +/-1 deg F. Worrying about 1 deg F difference is just a silly waste of time.

 

[david339933]

Well said jmec87. If it's A420 then it is A420, also remember B31.3 doesn't require MTRs. If it is stamped A420/ASME B16.X/MSS SPXX then that is good.
SWComposites, get your point, but you absolutely know the accuracy of any measuring items during the test. Calibration reports will tell you.

This is somewhat silly.....even for engineers.

 

[gwalkerb]

Thanks everyone. The MTRs are technically non-compliant as they don't specify values in both unit systems, but they do specify both the USC and SI material specs. The customer agreed to rate the piping system to -49F to avoid any issues.

Overall, I agree that this was a bit silly, but sometimes these small silly things end up holding up a lot of things until they are resolved.